5.56 Flat Primers

I can't tell for sure, but in the second photo it looks like the new primer isn't seated far enough into the case. If the fired primer is like that it could have been flattened by the bolt without an over pressure issue.

What projectile were you loading for?

.40

JCSC said:

These are for 223 / 556. It’s a multi chamber AR

Click to expand...

Ok, but was the primer standing proud of the head stamp? What weight projectile were you loading?

.40

For that weight projectile 23.7gr of H335 should have been fine. Sierra is showing a max load of 25.7 for that combination.

I still think the primer wasn't seated far enough. Should be a couple of thousands below flush.

.40

It's often recommended that you use CCI #41 (or equivalent) primers in AR's, which have very hard cups, because of the floating firing pin (which will often lightly dimple a primer upon chambering).

I suspect the "factory" round you have there is using a very hard primer. If you're just using standard SRP's, you might expect a little more deformation from the same pressure. It's a little hard to tell from straight-on photos, but I don't particularly see anything alarming in those primers. Can you get a pic from a 45° angle? Or maybe a pic of one of the used primers after de-priming?

I don't see a flattened primer in any of the 2 pics. When the primer is flattened by pressure, you'll know it.
The edges will be feathered onto the head of the cartridge, with no discernable corner.

The first pic, second from the left. That primer clearly shows the still rounded edges of the primer, and that is the worst of the bunch, from what I see.

I don't see a flattened primer.

For standard SRP's, I don't think that's flattening.* I think you're getting a false sense by comparing to a hard-cup primer (CCI #41's are brass-colored).

I would also observe that the swaging/chamfering of the primer pocket looks pretty aggressive, although photos can be deceiving.

Other than these primers, is there anything else that is giving you cause for concern?

* Obviously there is some modest deformation, but that doesn't appear out of the ordinary.

Have you checked your OAL to see if your into the lands? That would be the only reason to run higher pressure. Also Mil brass normally has less volume than commercial and sometimes require a a reduced load.

Those primers are not all that bad, as others have said.

It is an absolutely fruitless and nonsensical exercise to try to read primer flatness if the cases were not lubricated before firing.

Let me explain. These are fired cases in a bolt gun, the cases were dry, the chamber was dry, and the primers backed out. There was a lot of case to chamber friction and the load was so light, that the case sidewalls did not stretch to the bolt face.




Now, in your gas gun, what is obvious is that you had a lot of case to chamber friction. When your primers ignited they also backed out to the bolt face, and as pressures increased, pressures inside the cases were enough to stretch the case walls to the bolt face, and stuff the primers back in the case. The primers look flat, and it is not due to internal case pressure alone.

I found this out when I started lubricating my 308 LC cases in my M1a's. Loads that showed flat primers with dry cases and dry chambers, once the cases were lubricated, the primers were rounded after ejection. Obviously slathering grease on the outside of the case did not reduce combustion pressures, at least not that much, so something else was going on. What was going on was that lubrication broke the friction between case and chamber, so as combustion pressures rose, the case slide back to the bolt face, at a low enough pressure, that when the primer was stuffed back in, it was not expanded, and primer edges stayed rounded.

So, if you want to attempt to read primer flatness, the only valid procedure to follow is to grease your cases, and fire them. Then examine primer flatness. You don't need a lot of grease/oil, about the same amount you use when sizing cases. The shooter I learned this from, he never removed the RCBS case lube from his cases. He shot them, lubed them, sized, primed, charged, and put a bullet in the case. His cases felt slightly greasy, like you sneezed on them sort of greasy. That is all you need. Once the cases are lubed, you can see the transition from rounded primers to flat primers as charges increase. I know, I have done this. I shoot lubricated cases all the time. I want to see the transition, regardless of whether I am shooting gas guns or bolt guns.

Are you sure that the primer crimp is all gone? I've had issues with seating standard primers when some of the crimp is still there. Pic 2 looks like primer is touching unremoved crimp. It could be just my eyes though.

These I did today. Aguila 5.56 NATO.

I think you may be worried about nothing.
Those primers don't look especially worrisome to me.
Infact, I'd be happy with those results.

And remember a flattened primer may or may not be a symptom of over pressure.

JCSC said:

I know this has been discussed before, but I am scratching my head.

I was looking for a plinking load for the AR and reviewed several forums and handbooks, with the intention if using H335.

I loaded a first batch of 10 pcs to take along with me to the range and see if it would cycle decent. This was an AR pistol, 10.5" barrel. PSA factory barrel / BCG kit. Note that the gold primer is a factory range brass I grabbed. not from this gun, but it looked like what I would expect to see.
The pictures are from a second batch of H335 at 23.7gr. Everything I have read says people use 25+ without issue.
View attachment 851903 View attachment 851904

The 10 pcs consisted of mixed range brass, full length sized, trimmed, deburr ID/OD, swagged and chamfered. Powder was 24 gr H335 measured on my RCBS beam scale. I checked zero before and after as usual and weighed one of the 55gr Hornady FMJ-BT WC #2267, just as a habit. Primers are CCI 400 with a COL of 2.210/2.214 range.

My primers are smashed flat, as if they flowed into the primer pocket chamfer. No cratering, or raised areas around the pin, but not healthy looking.


For my own sanity, I took my 30 caliber hornady comparator as, to check a consistent shoulder length on these 6 fired pcs. The reference number was 1.499 / 1.500. I checked several resized pcs to see if I was pushing back the shoulders. they ranged 1.494/1.493.

I have some more 400 primers as well as some rem 7-1/2.

Thoughts?

Click to expand...

It looks like the crimp on the 2 middle cases was not removed. You might have slightly flattened the primers when you installed them. Those primers really are not all the flat and I don't see any flow.

Give the Remington 7 1/2 primers a try in your next batch and try using commercial brass with no crimp instead of the LC brass or Federal brass with a crimp.

I think you will find that the the soft small rifle primers (CCI-400, Federal 205, Winchester) will show flattening much sooner than the thicker cup primers (CCI-450, RP 7 1/2, CCI-41, Wolf 223, Federal AR Match). It is very obvious when you load to published 5.56 NATO pressures. The CCI-450 and Remington 7 1/2 primers appear fine and I saw definite flattening with CCI-400 primers.
Try identical loads to the CCI-400 loads you showed in your post, but use the Remington 7 1/2 primers and see if they make a significant difference. I am betting you will.

JCSC said:

I tried my best to remove those crimps. The swagger die sticks, so it’s a job.

Click to expand...

I had problems finding a good one that worked well. Take a look at this offering from CH4D. Best swagger on the market IMHO.

.40

I don't see anything in your pictures that would worry me. I agree with the others that your crimp may not be completely removed. Crimped primers can be a pain. All crimps are not the same and no one single method works perfectly on all of them. The swage feature on the Dillon 1050 probably comes the closest. I personally prefer to ream them.

Trying to avoid this.....

^ Now that's flat.

Your primers are not "flat"; far from it. Like the others, I suspect you are having issues fully seating the primer due to the military crimp being in place.



If you dislike your primer pocket swager, a much easier method is to simply buy a single-flute countersink tool, like used with flat head screws. Install this in a drill press or electric drill motor, and offer each de-primed case to the cutter for 1 second. A single-flute cutter leaves a clean bevel that guides the primer into place just as nicely as the rounded corner left by the swager tool, but with much less effort.

Or you can go buy the RCBS motorized Trim Mate "Case Prep Center" and do the same thing for $110 more. https://www.midwayusa.com/product/1458277820/rcbs-trim-mate-case-prep-center